Silver image stabilization with noble metal compounds and enediol developers

ABSTRACT

The present invention relates to a novel photographic film unit adapted to provide silver images of enhanced image stability which comprises photosensitive silver halide, a noble metal compound containing a noble metal ion below silver in the Electromotive Force Series of Elements, and a silver halide developing agent whose oxidation product is substantially nonoxidative to the thus-formed silver image for a time sufficient to enable the noble metal ion to contact said silver image to provide sustained and long-lasting stabilization effects.

United States Patent Land et a1.

[in 3,821,000 June 28, 1974 22] Filed: Nov. 7, 1972 21] Appl. No.:304,489

Related US. Application Data [63] Continuation-impart of Ser. No.145,044, May 19,

1971, Pat. N0. 3,730,716.

52 u,.s.. ci..... 96/76 R, 96/48 PD, 96/50 R [51] Int. Cl G03c 1/48 58Field of Search 96/29, 76, 4s PD, 50 R [56] References Cited UNITEDSTATES PATENTS 3,615,440 10/1971 Bloom .L 96/29 11/1972 Land et a1 96/76R 5/1973 Land 96/76 R Primary Examiner-Ronald H. Smith AssistantExaminer-.lohn L. Goodrow Attorney, Agent, or Firm-Robert M. Ford IABSTRACT The present invention relates to a novel photographic film unitadapted to provide silver images of enhanced image stability whichcomprises photosensitive silver 7 halide, a noble metal compoundcontaining a noble metal ion below silver in the Electromotive ForceSeries of Elements, and a silver halide developing agent whose oxidationproduct is substantially nonoxidative to thethus-formed silver image fora time suffi'cient to enable the noble metalion to contact said silverimage to provide sustained and long-lasting stabilization effects.

26 Claims, No Drawings SILVER IMAGE STABILIZATION WITH NOBLE METALCOMPOUNDS AND ENEDIOL DEVELOPERS CROSS REFERENCE TO OTHER APPLICATIONSThis application is a continuation-impart of application Ser. No.145,044, filed May 19, 1971 now US. Pat. No. 3,730,716.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention is directed to providing new and improved silver and additivecolor diffusion transfer process photographic film units whichpreferably comprise a composite photosensitive element adaptedtoprovide, as a function of the point-to-point degree of the element'sphotoexposure, integral negative and positive silver images whichinclude a negative silver image in superposed relationship with apositive silver image.

2. Description of Prior Art I In a composite print produced inaccordance with the g disclosure of the cited patent, the covering powerof a given mass of image silver in the print-receiving element is therestated to range from 14 to 15 times that of an equal mass of imagesilver in the silver halide element and, that for transparencyemployment, a maxi- 40 mum negative density of as high as 1.0 densityunits may be permissible where the maximum positive density is aboutfour or more times as great.

' The image-receiving element so employed is disclosed to be constitutedas to provide an unusually effective silver precipitating environmentwhich causes thesilver deposited therein, in comparison with negativesilver developed in the silver halide layer, to possessan'extraordinarily high covering power, that is, opacity per given massof reduced silver; see Edwin H. Land, One Step Photography, PhotographicJournal, Section A., pp. 7-15, January, 1950.

Specifically, to provide such envirnoment, silver precipitation nucleiare disclosed to be disposed within the silver receptive stratum inclusters possessing a diameter directly proportional to the mass ofimage silver to be deposited in situ by reduction. Such conformation isemployed to cause image silver to precipitate, in as sociation with thesilver precipitation nuclei clusters, with the required density and of asize directly related to the physical parameters of the clusters and theimage silver thus precipitated, in situ, in galaxies of chosen physicalparameters to provide image conformation in which the elemental silverof the image-receiving ele 65 ment may possess a very high order ofcovering power, for example, five to fifteen or more times that of thenegative image silver in the silver halide layer.

. 2 In accordance with the disclosures of US. Pat. Nos. 2,726,154 and2,944,894 additive multicolor reproduction may be accomplished by adiffusion transfer reversal process which specifically includes exposureof an 5 integral multilayer film assemblage through an optical screencomprising a plurality of minute optical elements and carryingphotosensitive and image-receptive layers. As disclosed, diffusiontransfer processing may be accomplished by permeation of thephotoexposed 0 integral film unit with a fluid processing compositionand the image-receptive layer retained in permanent fixed relationshipto the screen during, and subsequent to, formation of the requisitetransfer image, with the operators option of separating thephotosensitive layer from the remainder of the film unit, subsequent totransfer image formation, in film unit structures possessing theimage-receiving layer intermediate the screen and emulsion components.

lntegral additive color diffusion transfer film assemblages, essentiallycomprising photoresponsive material directly providing positive imageformation and possessing the sensitivity to incident electromagneticradiation and acuity of image formation necessary to effectively providecolor photographic image reproduction,

are disclosed and claimed in the following United States Patents whichare directed, in general, to film unit assemblages which comprise apermanently fixed laminate including a support carrying on one surfacean additive color screen, photosensitive silver halide and silverprecipitating nuclei:

US. Patents Nos. Issue Date 3,536,483 October 27, 1970 3,615,427 October26, 1971 3,615,428 October 26, 1971 3,615,429 7 October 26, 19713,615,426 October26, 1971 -sessing optical density inverselyproportional to exposure of the photosensitive silver halide layer,andspecifically, in a concentration adapted to provide a silver imagederived from unexposed silver halide crystals possessing greatercovering power than that of corresponding silver image derived fromidentical quantum of exposed silver halide crystals.

As set forth in the above-indicated patents improved image reproductionmay be obtained by means of the improved silver image characteristicsprovided therein.

Specifically, the above-indicated applications state that compositenegative/positive silver image formation possessing an optical densityinversely proportional to photoexposure of a photosensitive silverhalide-layer. characterized by improved silver image minimum and maximumoptical densities and image acuity may be achieved by a process whichincludes exposing a photographic film unit, which comprises a permanentlaminate containing a support carrying on one surface silverprecipitating nuclei and photosensitive silver halide, and processingthe film unit by contact, simultaneous with, or subsequent to, exposure,with an aqueous processing composition, containing a silver halidedeveloping agent and a silver halide solvent, to provide to he film unitthe direct formation of a silver image possessing particularly desiredlow minimum silver image optical density, in terms of exposed areas ofthe film unit, and high maximum silver image optical density, in termsof unexposed areas of the film unit, as a function of exposure anddevelopment of the film unit.

The above-mentioned film units are disclosed to be particularlydesirable for employment as a cine film for motion picture projection byreason of the inherent ability to simply and effectively process such afilm, employing relatively simple and stable processing compositions,without the necessity of providing a process and apparatus specificallyadapted to effect stripping of a separate emulsion stratum from theremainder of the film unit to provide information recordation possessingthe image integrity in reproduction characteristics required foreffective employment of the film.

Such film assemblages are suitably employed in a cine film system suchas that described in US. Pat. No. 3,615,] 27, which includes a compactcine film cassette or container adapted to allow exposure of a filmassem blage as retained therein, subsequent processing of the film toprovide the desired image record and projection of the resultant imagerecord of other presentation for viewing purposes. Thus, th filmassemblage may be exposed, processed, dried it necessary, and projectedwithout transferring the film'from its original container to any othercontainer or even in effect removing the film from the originalcontainer. The cine film system of US. Pat. No. 3,615,127 includes afilm processing station whereupon the exposed film strip is transportedfrom a first storage reel, past an applicator where a moist processingcomposition to develop to a visible condition images recorded on thefilm is applied and thence to a second storage reel.

The processing composition may be applied to the film assemblage by avariety of methods such as, for example, doctor blades, extrusion heads,capillary applicators, wicks, and the like. The amount of processingcomposition applied to the assemblage should be controlled withinrelatively narrow limits, however, suffcient processing composition mustbe applied to adequately and completely permeate the assemblage to thedepth necessary and in the quantity necessary to provide and desiredimage conformation.

The processing composition employed will generally include an alkalinematerial, for example, sodium hydroxide, potassium hydroxide, sodiumcarbonate, or the like, and most preferably, in a concentrationproviding a pH to the processing composition in excess of about 12. Theprocessing composition may, if desired, contain the sole silver halidedeveloping agent or agents and/or solvent or solvents employed or silverhalide developing agent and/or solvent in addition to that disposed asin the film unit. The relative proportions of the agents comprising thedeveloping composition may be altered to suit the requirements of theoperator. Thus, the developing composition may be modified by theemployment of preservatives, alkalis, silver halide solvents, etc.,other than those specifically mentioned herein. When desirable it isalso contemplated to include in the developing composition componentssuch as restrainers, accelerators, and the like, and the concentrationof such agents may be varied over relatively wide range commensuratewith the art.

In the film units and processes set forth in the aboveindicated US. Pat.Nos. 2,726,154 and 2,944,894, and

' the above-indicated copending applications, a quantity of processingcomposition and reactants will'inevitably be retained within the filmunit, particularly if the image-receiving layer is maintained inpermanent rela tionship with the emulsion as well as the screen, andthis residuum may possess the capacity to deleteriously effect imagequality over an extended period of time, in addition to conventionalenvironmental degradation of image silver.

SUMMARY OF THE INVENTION The present invention is specifically directedto novel photographic film units uniquely adapted to provide silverimages possessing image stability substantially in The fonnation ofsilver images, either negative or positive silver images, in thephotosensitive element per se, or in an adjacent receiving layer,generally results in the almost immediate attack of the silver from avariety of sources, most importantly from any residual processingreagents which may be retained in contact with silver image, and alsoambient environmental conditions. Thus, to achieve any significant levelof stability, it has been generally preferred as far as possible toexclude air during the application of the processing composition, thatis, during the formation of the silver image, and to remove asthoroughly and promptly as possible any residual processing reagents andreaction products thereof. As stated above, however, many film units andprocesses do not permit such stabilizing precautions to be taken.

Copending applications Ser. Nos. 95,443, filed Dec. 7, 1970, nowabandoned, and 95,424 filed Dec. 7, 1970 now US. Pat. No. 3,704,126,issued Nov. 28, 1972 describe and claim the employment of certain noblemetal compounds in the stabilization of silver image's. By means of thepresent invention, still further enhancement of the stability of silverimages can be achieved by substantially eliminating the almost immediatedegradative attack on the silver image, thus preventing substantiallyany deterioration of the silver image to occur prior to the interactionof the aforementioned noble metal compounds with the silver image andthe resulting stabilization produced thereby.

The present invention is particularly suitable for use in the fomiationof silver images provided by photographic silver ditfusion transferprocesses. Thus, the present invention is uniquely adapted to providesilver transfer images possessing image stability in excess of thatprovided by the prior art process and which process comprises, inessence, exposing to incident actinic radiation a silver diffusiontransfer film unit which includes photosensitive silver halide andpreferably silver precipitating nuclei; contacting the exposed film unitwith a processing composition comprising a silver halide developingagent which provides an oxidation product which is substantiallynon-oxidative with respect to a silver image, thereby providing avisible silver image I to the unit as a function of the point-to-pointdegree of exposure thereof; and contacting the silver image with a noblemetal ion below silver in the Electromotive Force Series of Elements, ata concentration effective to enhance the stability of the silver image.If a transfer image is to be formed, a silver solvent is preferablyemployed. A preferred silver halide developing agent is an a, B-enediolsilver halide developing agent.

The film units of the present invention are specifically adapted toimprove silver image stability, particularly silver diffusion transferimage stability with respect to degradative attack by film unit retainedresidual processing reagents and environmental image contaminants,particularly when processing is carried out under conditions which donot exclude air, which conditions generally accelerate degradation ofimage sil- DETAILED DESCRIPTION OF THE INVENTION In accordance with thepresent invention, development of a latent image is carried out bycontacting an exposed film unit, comprising photosensitive silverhalide, with a silver halide developing agent, thereby providing asilver image as a function of the point-to-point degree of exposurethereof; and contacting said silver image with a noble metal ion belowsilver in the Electromotive Force Series of Elements, the oxidationproducts of said developing agent being substantially nonoxidative withrespect to saidsilver image for a time sufficient to permit said metalion to contact said silver image.

Thus, in the present invention, initial degradation of the silver imageis obviated by employing a silver halide developing agent of theaforementioned character, i.e., one whose oxidation product issubstantially nonoxidative to the silver of the image. Contrary to priorart systems, the silver image is not subject to immediate attack by theoxidation products of the developer, and, in addition, is protected fromthe degradative effects of residual processing reagents and reactionproducts and the environment. The above-described initial and immediateprotection obtains for a time sufficient to permit the noble metal ionto contact the silver image to provide the long term stabilityenhancement.

Thus, in the present invention, the silver halide developer forms, uponreduction of silver halide, oxidation products which are chemicallyincapable of interaction with image silver to regenerate, by a furtherredox reaction, silver ion.

The present invention is directed to the long term stabilization ofsilver images. The silver images may be formed on a receiving layerspatially separated from the photosensitive element i.e., formed bydiffusion transfer processing, by precipitation in said receiving layer,preferably by employing silver precipitating nuclei in said layer. i

The novel system of the present invention can also be employed toprovide enchanced stabilization of the silver image formed in thephotosensitive element, i.e., a negative silver image or a directpositive image As examples of suitable silver halide developing agents,mention may be made of the hydroxylamines, such as N,Ndiethylhydroxylamine, N ,N-diethoxyethyf hydroxylamine, and the a,B-enediols.

It should also be understood that an auxiliary developer, such asdiarninoorthocresol or tolylhydroquinone may also be employed in thepresent invention.

In a particularly preferred embodiment, the silver image is formed bydiffusion transfer processing, and the silver halide developing agent isan a, ,B-enediol.

As previously characterized, a silver diffusion transfer process may beemployed to provide a silver transfer image, which may comprise anintegral negative silver image in superposed relationship to a positivesilver image adapted to exhibit greater covering power than the negativeimage, by development of the latent image provided a photosensitivesilver halide element by exposure and, substantially contemporaneouswith such development, formation of a soluble silver complex by reactionof a silver halide solvent with unexposed and undeveloped silver halideof the element. The silver of the resultant soluble silver complex is,at least in part,

precipitated in the presence of silver precipitating nuclei to providethe requisite positive silver image formation, which may optionally beretained in contiguous relationship to a negative silver image resultantfrom development of the latent image carried by exposed silver halideand the concomitant reduction of exposed silver halide to negative imagesilver, or separated therefrom subsequent to substantial transfer imageformation.

In accordance with a preferred embodiment of the present invention,development of the latent image is carried out by contacting the exposedfilm unit with an a, B-enediol silver halide developing agent andcontact ing the thus-formed transfer silver image with a noble metal ionbelow silver in the Electromotive Force Series of Elements. Enhancedstability, of a degree heretofore unobtainable, is thereby provided tothe image silver by employing the novel system of the present invention, i.e., the onfl-enediol silver halide developing agent and thenoble metal ion, even under processing conditions generally consideredto be most detrimental to film unit stability, particularly image silverstability, namely under conditions where air is not excluded as when theprocessing composition is flowed, sprayed or doctored onto the exposedfilm unit,

The a, B-enediol silver halide developing agent may be disposedinitially in the film unit, i.e., prior to expo sure of the film unit,or applied subsequent to exposure, for example, with the processingcomposition. The enediol developing agent may be disposed-in anysuitable is (in and wherein said segment does not form part of anaromatic ring Thus, catechol, for example, is specifically excluded fromthe class of developing agents defined herein. It should be understoodthat the term, a, B-enediol, as used herein, is intended to refer to theaboveindicated segment as well as the tautomer of said segment.

H see (in ii The enediol developing agents suitable for use in thepresent invention preferably contain the aboveindicated segment as aportion of a heterocyclic or carbocyclic ring.

In a particularly preferred embodiment, the a, B-enediols contain asegment of the formula:

As examples amnesia aja'sneaia mention may be made of the following:

ascorbic acid isoascorbic acid hydroxytetronic 'cidi" i dihydroxyacetone 46H. bis/gurus, CHa(. JCCHs dimethyl re duc ton e 7 OH OH iJH=bH-cH0 triose reducton ei V 7 In a particularly preferred embodiment,the enediol silver halide developing agent comprises substitutedreductic acid compounds of the formula:

un in-l OH wherein R, R", R' and R" each are selected from the groupconsisting of hydrogen and the radical -CH R"" wherein R"" is hydrogenor a monovalent organic radical selected from the group consisting ofamino. cyano. halo. hydroxyl, carboxyl, sulfonyl, alkyl, cycloulkyl,aryl of the benzene or naphthalene series and alkuryl of the benzene ornaphthalene series, at least one of said R, R", R' and R"" being -CHR"".

Of the above-indicated class of substituted reductic acids, thepreferred is tetramethyl reductic acid 8 (II -Ia cHt 0H CH3 OH CH3 6 iIt should be understood that the enediol silver halide developing agentmay also be employed in an inactive condition, particularly if suchdevelopers are to be disposed in the film unit to avoid fogging orstaining on storage. Such inactive species may be provided by acylatingthe hydroxyl groups, i.e., blocking said hydroxyl groups whichgroupswhich would be removedto regenerate the hydroxyl groups by theaction of an alkaline processing composition.- I

It is beilieved that the a, B-enediol developing agents contribute tothe enhanced stability of the image silver in combination with the noblemetal ion by virtue of the formation of oxidation products which arerelatively inert or innocuous with respect to the image silver. Thus,while prior art silver halide developers would form oxidation productsdeleterious to the image silver and which would result in attack on theimage silver substantially immediately upon processing, particularly inthe presence of air and retained residual processing reagents, the inertoxidation products of the enediol developers with the noble metal ionimparts a degree-of stability heretofore unobtainable, particularlyunder a normally adverse environment for image silver stability.

The noble metal may be provided to the silver transfer image by theemployment of a noble metal ion donor compound which is preferablysoluble in the processing composition selected to effect the diffusiontransfer process, but which when predisposed in the film unit forsolubilization by the composition is substantially insoluble in the filmunit medium within which it is disposed during storage and mostpreferably is solubilized at a rate particularly adapted to avoiddeleterious interaction during the initial stage in the development oflatent image impressed upon the film units silver halide byphotoexposure. Commensurate with the employment of conventional alkalineprocessing compositions and the substantially neutral pH environment ofsilver diffusion transfer film unit sheet eleactive than silver, i.e.,below silver in the Electromotive, Force Series of Elements and X is acomplexing ligand, preferably an organic ligand, which in the preferredembodiments of the invention provides a substantially water-insolublecomplex.

The noble metal ions required are those from metals less reactive thansilver, that is, those below silver in the Electromotive Force Series ofElements, preferably,

palladium, platinum and gold and most preferably Auf and Au.

The particular organic ligand preferably selected will be one which willstrongly bond to both the noble metal ion with which it is initiallyassociated and also silver ion displaced from the positive image, shouldimpart a relatively low degree of water solubility to the complex andmust not deleteriously interfere with the photo graphic utility of thefilm unit.

As will be further described in specific detail below, and subject tothe criteria set forth herein, the selected noble metal compound may bedisposed in various locations in the film unit such as, for example, inthe photosensitive layer, in the image-receiving layer, in a separatelayer, or in the processing composition, recognizing that the compoundmust be selected to avoid any deleterious sensitometric effect to thefilm unit or interference with positive silver image formation, and mustbe stable in the particular environment in which it is disposed, e.g,.in an alkaline processing composition medium.

In a particularly preferred embodiment of the present invention, anorganic ligand is selected which is a sulfur containing moiety sincesuch ligands possess a specifically desired affinity for noblemetalions. Particularly preferred for such ligands are sulfur atom containingheterocyclic moities which form stable, substantially water-insolubleorganometal compounds with. noble metals, and particularly those ligandswhich possess a preferential affinity for silver ions.

As examples of ligands contemplated for employment in the practice ofthe present invention, mention may be made of: r

2-mercaptobenzimidazole, 2- mercaptoacetamidothiadiazole, Z-mercapto-N-methylimidazole, Z-mercaptobenzothiazole, 2-mercaptobenzoxazole, l-(3,5'-dicarboxyphenyl)-5-mercaptotetrazole, l-phenyl-S- mercaptotetrazole,2-mercaptobenzselenazole, phenanthroline, 2,2'-dipyridyl,8-aminoquinoline, and the like.

In general, it has been found that the substantially water-insolublenoble metal compounds employed in accordance with the present inventionmay be added to the film unit at any stage during its manufacture. Theaddition, therefor, may be made before, during or subsequent tofabrication of the film unit although, as stated herein, the compoundwill preferably be added as a coating final to, for example, thephotosensitive silver halide coating solution prior to itsapplication toa supporting member. It will be recognized that the noble metal compoundemployed in accordancewith the invention may also be utilized incombination with additional known image modifying adjuvants such astoning agents, and the like, where desired.

ln the preferred embodiment of the present invention, the moble metalcompound must be substantially water-insoluble. that is, sufficientlyinsoluble in the aqueous media constituting the film unit as to preventdeleterious sensiometric interaction between photosensitive silverhalide and the noble metal compound during storage, exposure and initialcritical stages inthe processing of the unit. In general, the compoundse lected will preferably possess a solubility in water of less thanabout 10 5 moles/liter and will most preferably be adapted to besolubilized by processing composition, for example, alkaline processingcomposition, at a rate ineffective to interfere with the constitution of10 and for the development of latent image carried by photoexposedsilver halide.

As examples of suitable noble metal compounds, contemplated foremployment in the practice of the present invention, mention may be madeof organometal compounds such as, for example, goldmercaptobenzimidazole, gold mercaptoacetimidothiazole, goldmercapto-N-methylimidazole, gold phenylmercaptotetrazole, etc., andinorganic noble metal compounds such as, for example,

gold thiourea, gold thiocyanate, gold chloride, sodium chloroaurate,etc., and corresponding platinum, palladium, and the like, noble metalanalogues.

In general, the optimum concentration of compound to be employed shouldbe determined empirically for each specific photographic film unitsystem. However,.

' image below the beneficial level generally sought, but

does not obliterate obtaining beneficial stabilization re sults. r

In point of fact, advantageous results are obtained employing minimalconcentrations of compound adapted, to provide a metal ion interchangewith mini mal quantities of elemental image silver.

While not intending to be bound by theory, it is believed that partialreplacement of elemental image silver by the selected noble metal iondonated by the compound provides a decrease in the reactivity of theimage silver with respect to interaction with degradative materialsprovided by residual processing reagent present in the film unit or theenvironment. Specifically, in the preferred embodiments of the presentinvention, silver ions derived from image silver may be displaced bynoble metal ions derived from the compound by a'redox reactionresultingin the generation of noble metal and complexed silver ions thusprovidadapted to provide positive silver image formation in aratedtherefrom, and film units which comprise structures adapted to providedirect positive silver image formation such as, for example, film unitspossessing silver precipitating nuclei directly associated withphotosensitive silver halide.

As will be readily recognized, additional layers may be optionallyincluded in the film unit such as, for example, a separate layerretaining the noble metal donor of the present invention as well asspacer layers, barrier layers, protective layers, stripping layers, andsupport layers.

In the preferred embodiment of the present invention the film unitcomprises a support preferably transparent to actinic radiation andcarrying on a first surface a photosensitive silver halide layer and alayer containing silver precipitating nuclei dispersed therein and, forcolor image reproduction, an additive color screen is interposed betweenthe transparent support and the photosensitive silver halide layer.

Employment of the preferred organometal complexes or compounds whereinthe ligand is an organic sulfur-containing heterocyclic ligand of thetype which acts as a silver halide photographic stabilizing agent mayeffectively enhance storage stability of the film unit in which thecomplex is disposed. Thus, rather than inducing deleterious effects tothe film in which itis disposed, the noble metal complex mayadditionally provide resistance to the normal storage fog degradationgenerally encountered in silver halide emulsions.

As will be readily recognized, the metal ion donor may also be locatedin whole or in part in a separate layer in the film unit, preferablyadjacent to the layer in which the image silver is to be located;directly in the image-receiving layer and associated with the silverprecipitating nuclei, or in the liquid processing composition, and aplurality of donors may be optionally employed, which donors may bedisposed, individually or in combination, at one or more of suchlocations. As stated above, in the instance that the donor is disposedin the processing composition, the specific ligand should be selected toavoid any deg'radative effects which may occur during storage'in thespecific media of the processing composition, generally a highlyalkaline medium. In instances where is is desired is distribute a noblemetal ion donor to the silver image by means of a processing compositionin which it fails to exhibit required storage stability, the donor maybe initially disposed in association with a selected processingcomposition applicator such that it is solubilized by and incorporatedin the composition immediately preceding, or during, application of thecomposition to the film unit as, for example, initially disposed in aprocessing composition applicator wick which provides the transportconduit between the storage chamber for the composition and the filmunit during processing.

In addition to the above-mentioned stabilization properties, that is,stabilization of silver image quality and resistance to degradation ofthe silver image from resistance to degradation of the silver image fromresidual reagent and atmospheric contact, it has also been discoveredthat visual image quality with respect to 12 toning may be achieved suchas to provide a blacker or more neutral silver image.

In a plurality of the above-described film units, the negative silver isalso'avail'able for interaction with the noble metal, particularly wherean integral unit is employed or where the metal donor is initiallydisposed in the photosensitive silver halide layer. In such units,although the entire amount of silver initially in the unit remainspresent, in composite film unit structures the negative silver is notvisually present to the observer by reason of the difference in coveringpower and physical state between the respective positive image silverand the negative image silver. It is believed that by reason of, forexample, covering power and physical state, in-

cluding surface area of individual image silver particles, the presentinvention is preferentially effective with respect to effectingstabilization of the desired positive transfer silver image possessingthe physical character described above, without appreciable deleteriouseffect with respect to the covering power of either the negative or thepositive silver image. In addition, it is understood that negative imagemay act as a deposition matrix to effect removal, from the activephotographic system, .of noble metal ionin excess of that required toeffect stabilization of the positive silver image.

Although as previously stated, a specifically preferred noble metal ioncomprises gold ions, it has been found that the employment of the statedmetal does not result in the deposition of red gold contaminating imageintegrity. Thus, the photographic quality of the image is not impairedby extraneous reactions of the preferred metal ion and the goldcomponent has not been found to deposit on, or to interfere with, theoperation of conventional silver transfer image nucleating sites.

In the practice of the present invention, the silver precipitatingnuclei may be disposed within the photosensitive silver halide stratumof the film unit assemblages, in a separate layer or layers or elementcontiguous one or both surfaces of the silver halide stratum and thesilver halide stratum may comprise two or more silver halide strata,each optionally retaining silver precipitating nuclei, and may include aseparate silver precipitating nuclei layer positioned intermediateseparate silver halide strata.

For the purpose of insuring the production of a positive imagepossessing a high covering power, the silver precipitating nuclei willbe disposed within the film unit in a concentration per unit areaeffective to cause image silver derived from unexposed silver halidecrystals to possess the desired opacity per given mass of in situreduced silver.

In general, silver precipitating nuclei comprise a specific class ofadjuncts well known in the art as adapted to effect catalytic reductionof solubilized silver halide specifically including heavy metals andheavy metal compounds such as'the metals of Groups IB, IIB, IVA, VIA,and VIII and the reaction products of Groups IB, IIB, IVA, and VIIImetals with elements of Group VIA, and may be effectively employed inthe conventional concentrations traditionally employed in the art, preferably in a relatively low concentration in the order of about I 25 X 10moles/ft? Especially suitable as silver precipitating agents are thosedisclosed in US. Pat. No. 2,698,237 and specifically the metallicsulfides and selenides, there detailed, these terms being understood toinclude the selenosulfides, the polysulfides, and the polyselenides.Preferred in this group are the so-called heavy metal sulfides. For bestresults it is preferred to employ sulfides whose solubility products inan aqueous medium at approximately 20 C. vary between 10," and andespecifally the salts of zinc, copper, cadium and lead. Alsoparticularly suitable as precipitating agents are heavy metals such assilver, gold, platinum, palladium, etc., and in this category the noblemetals illustrated are preferred and are generally provided in thematrix as colloidal particles. 7

In particular, it has been discovered that improved color reproductionin accordance with the principles of additive color photography may beobtained by means of the improved image characteristics provided byreason of the present invention. Specifically, it has been found thatcomposite negative/positive silver image formation, particularly adaptedfor additive color reproduction and characterized by improved silverimage minimum and maximum optical densities and image acuity may beachieved by a process which includes exposing a photographic film unit,which comprises a color screen in association with a photosensitivesilver halide layer fabricated to conform to the parameters previouslyset forth and having associated therewith silver precipitating nuclei,wherein the exposure of the emulsion is effected by radiation traversingthrough the color screen and the processing of the film is accomplishedby contact, simultaneous with, or subsequent to, exposure, with anaqueous processing composition, containing a silver halide developingagent and a silver halide solvent, to provide to the film unit thedirect formation of a silver image possessing required low silver imageoptical density, in terms of exposed areas of the film unit, andrequired high silver image optical density, in terms of unexposed areasof the film unit, as a function of exposure and development of the filmunit.

Color photographic reproduction may thus be provided by exposing theabove described photoresponsive silver halide stratum, to selectedsubject matter, through an optical screen element possessing f ltermedia or screen elements of selected radiation modulatingcharacteristics such as filter media selectively transmittingpredetermined portions of the electromagnetic radiation spectrumsvisible segment. The color information thus recorded is read out byviewing resultant image conformation through the same or a similarscreen element in appropriate registration with the image. Theindividual filter media or screen elements constituting the opticalscreen willbe constructed to effect selective filtration ofpredetermined portions of the visible electromagnetic spectrumsubstantially corresponding to its red, blue and green regions and colorinformation recordation will-be accomplished by pointtopoint incidenceof radiation actinic to the selected photoresponsive materialasmodulated by such screen element. Visual reproduction of the informationcontent recorded is accomplished by read out of the impressed image asmodulated by the original or a sub stantially identical screen elementin accurate registration with the image record.

Although for color information recordation purposes, the photoresponsivematerial and optical screen may comprise separate and distinct elementsappropriately registered during periods of exposure and viewing and theoptical screen element may be temporarily or I respect to and/orprotected from contact with the propermanently positioned onthe surfaceof a transparent carrier opposite that retaining the photoresponsivematerial, for practical purposes, it is preferred to permanentlyposition the photoresponsive material in direct contiguous relationshipto the color screen during exposure, in order to maximize the acuity ofthe resultant image record;

Subsequent to exposure of the photoresponsive material to actinicradiation transmitted through and ti]- tered by the optical screen, theresultant photoexposed element may be further processed in accordancewith the materials selected and generally without regard to the filterscreen when the latter-element is stable with cessing compositions andcomponents selected. Such protection and stability will ordinarily beenhanced and facilitated by dispositionof the filter screen between atransparent, processing composition impermeable carrier and thephotoresponsive material, and, in particular, where such configurationadditionally includes the presence of a processing composition barrierelement or layer intermediate the screen and the photoresponsivematerial.

The preferred film assemblages will comprise a panchromaticallysensitized silver halide stratum possessing the parameters previouslyset forth positioned contiguous a surface of the multicolor additivecolor screen which, in the preferred assemblage denoted above, may alsopossess' the image-receiving component intermediate a silver halidestratum and the color screen, to allow exposure of the emulsion to beaccomplished through a color screen, including through a transparentsupporting member, if present, and formation of the requisite positivesilver image in immediate, contiguous relationship to the color screenemployed during exposure. Such embodiment obviates the necessity ofregistering the color screen with the resultant positive silver image,for viewing purposes, in that the screen employed for exposing may alsobe employed for viewing and is in automatic registration with thepositive silver image.

Thus a preferred embodiment of the present invention for thereproduction of color information in accordance with the principles ofadditive color photography may comprise a film unit assemblage whichcontains an additive multicolor screen comprising a geometricallyrepeditive plurality of actinic radiation-filtering colored elementsincluding a set of primaryblue-colored filtered elements, a set ofprimary green-colored filter elements and a set of primary red-coloredfilter elements arranged in a repeditive distribution in side-bysiderelationship in a substantially single plane positioned intermediate atransparent support member and a photosensitive silver halide stratumconforming to the parameters set forth above and having silverprecipitating nuclei associated'therewith in any of the mannerspreviously detailed.

It will be specifically recognized, however, that in embodiments of theinvention which employ a separate photoinsensitive silver precipitatingnuclei containing layer, intermediate a color screen and aphotosensitive silver halide layer, such nuclei containing layer shouldmost preferably possess a thickness of less than about a wavelength oflight so that for all practical optical purposes the photosensitivesilver halide emulsion layer will be effectively located next adjacentthe color screen whereby minimizing to a maximum extent any possibleoptical parallex problems during radiation transmission, as well as anysubstantial lateral diffusion of silver image-forming components duringprocessing of the film unit.

The photoresponsive silver halide materials employed in the practice ofthe present invention will, as previously described, comprise a crystalof a compound of silver, for example, one or more of the silver halides,such as photosensitive silver chloride, silver iodide, silver bromide,and preferably, mixed silver halides, such as silver chlorobromide,silver iodochloride, silver iodobromide or silver iodochlorobromide, ofvarying halides ratios and the silver concentrations despersed in aprocessing composition permeable binder material such as gelatin and thelike, most preferably silver iodobromide and iodochlorobromide,particularly that comprising ,1 to 9 percent iodide by weight of silver.

, The preferred silver halide type photosensitive layers employed forthe fabrication of the photographic film unit, may be prepared byreacting a water-soluble silver halide, such as ammonium, potassium orsodium chloride, preferably together with corresponding iodide andbromide, in an aqueous solution of a pepti zing agent.

such as colloidal gelatin solution; digesting the dispersion at anelevated temperature, to provide increased crystal growth; washing theresultant dispersion to remove undesirable reaction products andresidual water-soluble salts, for example, employing the preferredgelatin matrix material, by chilling the dispersion, noodling the setdispersion, and washing the noodles with cold water, or, alternatively,employing any of the various floc systems, or procedures, adapted toeffect removal of undesired components, for example, the proceduresdescribed in US. Pat. Nos. 2,614,928; 2,624,929; 2,728,662, and "thelike; after ripening the dispersion at an elevated temperature incombination with the addition of gelatin or such other polymericmaterial as may be desired and various adjuncts, for example, chemicalsensitizing agents and the like; all according to the traditionalprocedures of the art, as described in-Neblette, C. B., Photography ltsMaterials and Processes, 6th Ed., 1962.

Optical sensitization and preferably panchromatic sensitization of theemulsions silver halide crystals may then be accomplished by contactwith optical sensitizing dye or dyes; all according to the traditionalprocedures of the art, or described in Hamer, F. M. The Cyanine Dyes andRelated Compounds.

Subsequent to optical sensitization, any further desired-additives, suchas coating aids and the like, may be incorporated in the emulsion andthe mixture coated according. to the conventional photographic emulsioncoating procedures known in the art. 1

As the binder for the photoresponsive material, the aforementionedgelatin may be, in whole or in part, replaced with some othernaturaland/or synthetic processing composition permeable polymericmaterial such as albumin; casein; or zein or resins such as cellulosederivative, as described in US. Pat. Nos. 2,322,085 and 2,541,474; vinylpolymeric such as described in an extensive multiplicity of readilyavailable U.S.and foreign patents or the photoresponsive material may bepresent substantially free of interstitial binding agent as described inUS. Pat. Nos. 2,945,771;

3,145,566; 3,142,567; Newman, Comment on Non- 16 Gelatin Film, B. J. O.P., 434, Sept. 15, 1961; and Belgian Pat. Nos. 642,577 and 642,558.

One procedure particularly useful for the production of one preferredgelatino silver halide emulsion comprises the formulation, in the mannerpreviously detailed, of a silver iodochlorobromide emulsion containingin order of 1 percent iodide by initially forming a silver chlorideemulsion, adding to the emulsion the requisite bromide and iodide,separating from the formulation undesired reaction products, andafterripening the resultant silver iodochlorobromide emulsion incombination with the selected auxiliary sensitizing, speed increasing,etc., adjuncts elected.

Specifically, the specified emulsion may be formulated by a conventionaldouble jet addition, over a period of 3 minutes and 25 seconds, at arate of 1,800 cc. per minute of 1,026 gms. of potassium chloride in5,336 gms. of distilled water at 60 C. and 2,000 gms. of silver nitratein 5,336 gms. of distilled water to a solution at C. comprising 205 gms.of potassium chloride, 5,750 gms. of distilled water and 2,560 gms. of asolution formed by dissolving 800 gms. of gelatin in 8,800 mls. ofdistilled water, adjusting the pH to l0i0.1 with 50 percent sodiumhydroxide, adding over a 30 minute period and at 40C. with stirring 88gms. of phthalic 'anhydride in 616 mls. of acetone, and after 30 minutesat 40 C. adjusting the pH to 6-with 50 percent sulfuric acid. After adigestion period of 5 minutes at 80 C., 60 gms.-of potassium iodide and1,337 gms. of potassium bromide in 5,336 gms. of water is added to theformulation, over a period of 3. minutes and 25 seconds, at a rate of1,800 cc. per minute and at 60 C. and the resultant emulsion digestedfor a further period of 35 minutes at80 C. The resultant silveriodochlorobromide emulsion is precipitated at 20 C. by reduction of thepH to about 2.7 with sulfuric acid, the precipitate separated from thesupernatant liquid and washed with chilled distilled water until thewash water exhibits a conductivity of 50 to p. mhos/cm, the volumeadjusted 'with distilled water for the addition of 950' gms. of gelatin,and the emulsion then afterripening for 210 minutes at a temperature of54 C. and a pH of 5.7.

The silver precipitating nuclei and/or discrete nuclei layer or layersmay be realized by the application of, location of, and/or in situgeneration of, the nuclei, which may be similar or dissimilar,directlyor indirectly in or as the respective layer and in the presenceor absence of binder or matrix material and, in the latter instance, maycomprise one or more adjacent or separate strata of a permeable materialcontaining one or more nuclei types disposed in one or more such layers.Matrix materials adapted for such employment may comprise both inorganicand organic materials, the latter type preferably comprising natural orsynthetic, processing composition permeable, polymeric materials such asprotein materials, for example, glues, 'gelatins, caseins, etc.,;carbohydrate materials, for example, chitins, gums, starches, alginates,etc.; synthetic polymeric materials, for example, of the vinyl orcellulosic types such as vinyl alcohols, amides and acrylamides,regenerated celluloses and celluloseether and esters, polyamides' andesters, etc., and the like; and the former type preferably comprisingsub'macroscopic agglomerates of minute particles of a water-insoluble,inorganic, preferably siliceous material such,for example, =as silicaaerogel as disclosed in US Pat. No. 2,698,237.

Where the silver precipitating agent is one or more of the heavy metalsulfides or selenides, it may be preferable to prevent the diffusion andwandering of the sulfide or selenide ions, as the case may be, by alsoincluding, in the silver precipitating layers or in separate layersclosely adjacent thereto, at least one metallic salt which issubstantially more soluble in the processing agent than the heavy metalsulfide or selenide used as the silver precipitating agent and which isirreducible in the processing agent. This more soluble salt has, as itscation, a metal whose ion forms sulfides or selenides which aredifficultly soluble in the processing agent and which give up theirsulfide or selenide ions to silver by displacement. Accordingly, in thepresence of sulfide or selenide ions the metal ions of the more solublesalts have the effect of immediately precipitating the sulfide orselenide ions from solution. These more soluble or ion-capturing saltsmay be soluble salts of any of the following metals: cadmium, cerium(ous), cobalt (ous), iron, lead, nickel, manganese, thorium and tin.Satisfactory soluble and stable salts of the above metals may be found,for example, among the following groups of salts: the acetates, thenitrates, the borates, the chlorides, the sulfates, the hydroxides, theformates, the citrates and the dithionates. The acetates and nitrates ofzinc, cadmium, nickel, and lead are preferred; In general, it is alsopreferable to use the white or lightly colored salts although forcertain special purposes the more darkly colored salts may be employed.

The previously mentioned ion-capturing salts may also serve a functionof improving the stability of the positive image provided they possess,in addition to the aforementioned characteristics, the requisitesspecified in US. Pat. No. 2,584,030. For example, if the ioncapturingsalt is a salt of a metal which slowly forms insoluble or slightlysoluble metallic hydroxides with the hydroxyl ions in the alkalineprocessing liquid, it will suitably control the alkalinity of the filmunit to substantially, if not totally, prevent the formation ofundesirable developer stains.

In accordance with a particularly preferred embodiment of the presentinvention, photosensitive and image-receiving strata carrying the imagesilver are fabricated to substantially prevent microscopic distortion ofthe image conformation by preventing microscopic migration or diffusionof image elements within the polymeric matrix. in general, conventionalphotographic image elements may ordinarily comprise a microscopicallydynamic system without seriously noticeable disadvantages totheconventional employment of the image. l-lowever, for particularlyaccurate color reproduction in accordance with the principles ofadditive color photography, microscopic distortionof image elements ispreferably obviated to insure maximization of the accuracy of imageregistration with the appropriate individual optical filter elements ofthe additive color screen associated with the image-carrying element.Specifically, it has been found that a photosensitive film unitcomprising photosensitive emulsion containing silver halide crystals andsilver precipitating nuclei dispersed in a polymeric binder and whereemployed photoinsensitive image-receiving layers containing silverprecipitating nuclei dispersed in a polymeric binder, the binders ofwhich possess a lattic effective to substantially prevent microscopicmigration or diffusion of image silver, provide color reproductionacuity particularly desired for effective color reproduction in themanner previously described.

The desired polymeric binder lattice property may be readily achieved byselection of a polymeric material possessing the property ofsufficiently fixing spacially image components, or a polymeric material,otherwise desired, may be modified, for example, by crosslinking and/orhardening, to the extent necessary to provide the desired spacialmaintenance of image components, that is, a rigidity effective tomaintain positive image components in registration with the individualoptical filter elements of the color screen through which thephotosensitive emulsion was exposed. For example, a preferred polymericbinder material, that is, gelatin, may be hardened by contact withconventional hardening agents to the extent necessary to provide thedesired rigidification of the photographic image. Where desired discreteparticulate materials facilitating increased processing compositionpenetration of the photosensitive element, without deleterious effect onthe polymeric matrixs lattice, may be advantageously in-,

corporated in the photosensitive element for the purpose of expeditingprocessing of the element.

Production of color screen, in accordance with the art may be preparedby totally mechanical means, as for example, by printing or ruling adyeable substrate, for example, with a greasy ink formulation, inaccordance with the'desired filter pattern, subjecting the substrate tosuitable coloration, in areas which do not possess the repellant inkmask, effecting removal of the mask, and repeating this procedure, inaccordance with the geometrical pattern of filter elements desired, asufficient number of times to provide the desired multiplicity ofdiversely colored filter element; directly printing a carrier substratewith the desired dye formulations in accordance with the predeterminedfilter pattern and repeating this printing procedure a sufficient numberof times to provide the multiplicity of colored filter elements desired,or depositing, as an irregular filter screen pattern, a thin layercomprising a random distribution of small grains, such as starch grains,which have been independently colored with the colors desired foroptical filtering effects. Alternatively, color screen may be preparedby photomechanical methods of the type initially proposed by, forexample, Ducos Du l-lauron in the nineteenth century, which comprise,in. general, coating a suitable support or film base with an adhesivecomposition having coated thereon a photosensitive colloid composition,as for example, dichromated gelatin, efi'ecting exposure of thesensitive gelatin layer by incident actinic radiation, through asuitable mask which provides an exposure pattern devised in accordancewith the desired optical filter element arrangement, effectingdifferential hardening of the sensitized material as a function of thepoint-to-point degree of exposure, removing unexposed unhardenedmaterial by solvent contact, subjecting the remaining hardened materialto a suitable dyeing procedure in order to, provide a first-coloredoptical filter element series, and repeating this procedure, employingappropriate masks, as often as necessary to provide the number ofoptical filter element types desired in the final color screen element.

Although color screen may be produced by traditional contact printing orprojection type photomechanical processes, a particularly preferredprocess for the production of color screen comprises the process setforth in US. Pat. No. 3,284,208 which includes, in essence, successivelycoating the smooth surface of a lenticular film with a plurality ofphotoresponsive layers and sequentially subjecting the coatings toselec' tively displaced radiation incident on, and focused by, thelenticules receiving same, in order to provide selective exposure of thecoating. Subsequent to each exposure, unexposed coating is removed andthe resultant resist dyed in order to provide a series of chromaticfilter elements, prior to the deposition of the next succeedingphotoresponsive layer. Each such exposure is derived fromelectromagnetic radiation incident on the lenticular film at an angulardisplacement specifically adapted to provide the desired plurality ofchromatic filter element series in substantial side-by-side or screenrelationship and adapted to filter predetermined wavelengths of light.

For the preparation of the preferred trichromatic additive screens, theexposed area of each photoresponsive area will generally comprise aboutone-third of the layer contiguous each lenticule receiving exposingradiation. Although all three exposures may be accomplished by radiationincident on the lenticules of the lenticular film at three separateangles each adapted to provide exposure about one-third of the areacontiguous each lenticule receiving radiaiton, it will be recognizedthat the terminal chromatic filter formation may also be provided byexposing the terminal photoresponsive layerrto diffuse radiationtraversing through the lenticular film and masked by the previouslyformed chromatic filter elements.

At a stage subsequent to formation of the first and second series offilter elements, the lenticular configuration will be constituted as acontinuous smooth surface. In the instances where the lenticulescomprise a separatestratum temporarily affixed to the surface of asupport on which the color screen is formed, such separate stratum maybe stripped from the support. Alternatively, where the lenticulescomprise an integral component of the film base or support and have beenprovided to the base by pressure and/or solvent deformation of the base,a continuous smooth surface may be reconstituted by application ofsuitable solvent and the deformation pressures produced during themanufacturing of lenticular film base released to provide reconsitutionof the bases original configuration. Where desired, for example, foroptical transmission purposes, the reconstituted surface may bepolished, for example, by surface contact with an appropriate rotatingpolishing cylinder or drum, for the time interval necessary to providethe desired optical characteristics to the film base surface.

Optionally the external surface of the color screen may be overcoatedwith a protective polymeric composition, such as nitrocellulose,cellulose acetate, and the like, for the purpose of protecting thescreen from processing composition deformation during employment of theresultant film unit. The external surface of the color screen may thenhave applied thereto the remaining layers constituting the filmassemblage as detailed hereinbefore.

Apparatus particularly adapted to facilitate effecting exposure of thelenticular film in accordance with the aforementioned US. Pat. No.3,284,208 is disclosed and claimed in US. Pat. No. 3,318,220.

The support or film base employed may comprise any of the various types.of transparent ridged of flexible supports, for example, glass,polymeric films of both the synthetic type and those derived fromnaturally oci acetatebutyrate, or acetate propionate; polycarbonates;polystyrenes; and the like.

The present invention will be illustrated in greater detailed inconjunction with the following illustrative constructions which setforth representive embodiments and photographic utilizations of the filmunits of the present invention, which however, are not limited to thedetails there set forth but are intended to be illustrative only.

The smooth surface of a lenticular film comprising a polyester film basemay have bonded to one surface a cellulose acetate butyrate layercomprising 550 lenticules per inch, each of which may possess aplanoconvex configuration for condensing the incident radiation intoconverging rays and a focal length generally in the order of about 100microns in air and, as a result of this short focal length, imagingobjects over about one inch from the lens surface at infinity, may becoated on the opposite surface with an adhesive composition comprisingcc. of methanol, 1.25 grams of nitrocellulose, and 30 cc. of butylalcohol. A first layer of gelatin sensitized by the addition of 15weight percent potassium dichromate (based on dry gelatin), may then becoated on the external surface of the first adhesive layer. The firstgelatin layer may then be exposed to ultraviolet radiation, inaccordance with the previously detailed explanation, and the resultantphotoexposed carrier subjected to a water wash in order to provideremoval of unexposed sensitized gelatin, in accordance with the exposurepattern contained in the first gelatin layer. The web may then betreated with an acid dyeing bath comprising 1.17 percent Direct Red Cl.81; 0.32 percent Direct Yellow Cl. 4; and 2.95 percent glacial aceticacid, rinsed to effect removal of excess dye, dried and a secondadhesive composition containing 70 cc. of methanol, 30 cc. of butylalcohol, and l .25 grams of nitrocellulose overcoated thereon. A secondlayer of gelatin sensitized by the addition of 15 weight percentpotassium dichromate may be coated on the second adhesive layer. Thesecond photosensitized gelatin layer may also be exposed to ultravioletradiation in accordance with the previously detailed description. Thesecond gelatin layer may then be washed with water to effect removal ofunexposed photosensitive gelatin, in the manner previously detailed, andthe remaining gelatin resist dyed by contact with an acid dyeing bathcontaining 0.83 percent Acid Green CI. 7; 0.32 percent Direct Yellow CI.4; and 2.86 percent glacial acetic acid. The web may then be rinsed toeffect removal of any residual excess dye, dried and coated with a thirdadhesive composition comprising 30 cc. butanol, 1.25 grams ofnitrocellulose, and 70 cc. of methanol. A third layer of gelatinsensitized with 15 weight percent potassium dichromate may then becoated on the external surface of the third adhesive layer and thethirdphotosensitive gelatin layer subjected to exposure by ultravioletradiation, in accordance with the description detailed previously. Thethird layer of photosensitive gelatin may then be washed in order toprovide the desired resist formation and the resultant resist dyed bycontact with a solution containing 1.0 percent Blue T Pina and 1 percentglacial acetic acid, washed toeffect removal of residual dye and dried.A protective overcoat layer may be provided by coating the externalsurface of the multicolor screen element with a composition comprising70 cc. methanol, 30 cc. butanol, and grams of nitrocellulose.

Subsequent to formation of the color screen, the lenticulated celluloseacetate butyrate may be removed from the polyester base and the externalsurface of the polymeric protective coating may be coated with acomposition comprising deacetylated chitin and copper sulfide at acoverage of about 4.4 mgs./ft. deacetylated chitin and 0.25 mgs./ft.copper sulfide. On the external surface of the silver precipitatingagent containing layer may then be coated a hardened gelatino silveriodobromide emulsion coatedat a coverage of 150 mgs./ft. gelatin and 100mgs./ft. silver and containing 7.4 mgs./ft. propylene glycol alginate,2.9

mgsjft. sodium dioctylsulfosuccinate and, overcoating the emulsionlayer, a layer of gelatin containinggold complex of the species and atthe concentration identifled below. l

The gelatino silver iodochlorobromide emulsion employed may be preparedas previously detailed and chemically sensitized, at-about 56C.,by theaddition of a sensitizing amount of a solutioncontaining 0.1 gram ofammonium thiocyanate in 9.9 cc. of water and 1.2 cc. of a solutioncontaining 0.097 gram of gold chloride in 9.9 cc. of water. Theresultant emulsion may then be panchromatically sensitized by thesequential addition of 0.1 percent, by weight, methanol solutions ofanhydro 5,5'-diphenyl-3,3' bis-(4- sulfobutyl)-9-ethyloxacarbocyaninehydroxide and anhydro 5,5 -dimethyl-3,3 -bis-( 3-sulfopropyl 9-ethyl-.

'thiacarbocyanine hydroxide in optionally effective concentrations.

The copper sulfide silverprecipitating agent may be provided in situ bythe addition of substantially equi- 22 molar diiantities of coppernitrate and sodium sulfide solutions to the deacetylated chitin coatingsolution prior to application of the composition to the color basesupport.

The film unit, fabricated either substantially as detailed above or inaccordance with any one or more of the structural embodiment denotedabove, may be subjected to exposing electromagnetic'radiation incidenton the transparent base and developed by temporary contact of the filmunit, for about seconds, with one of the processing compositionsidentified below to provide a positive silver image possessing theoptical characteristics described hereinbefore and the acuity re quiredfor additive color reproduction.

Processing Composition A 1624 cc. water silver halide developer Forpurposes of illustrating the advantageous results achieved by reason ofthe present invention, film units,

fabricated and processed in the general manner detailed above, weresubjected to an accelerated aging test which comprised the exposure ofprocessed units 1 to an environmental temperature of 100F. at a relativehumidity of 100 percent, for 72 hours.

The following tables set forth the density of the indicated component oftransmitted lightas measured on a densitometer.

TABLE 1 The film units were processed with Processing Composition-A plusthe indicated developers and 0.02 g./l0 cc. of processing composition ofdiamino orthocresol as an auxiliary developer.

86.1 mg. silver/9.6 mg. gold 92 mg. silver/No gold compoundMereaptobenzirnidazole Red Green Blue Red Green Blue Toluhy droq uinoneN (0.423 g.ll0 cc. of processing composition) before test 2.1? 2.31 3.072.25 2.65 3.05

after .49 1.06 .90 2.05 1.06 V 2.66

' '71 of original v D retained 23 38 29 91 '70 87 Dimethylhydroquinone vt V (0.47 g./l0 cc. of processing composition) berm lest 1.03 1.54 1.801.54 2.06 2.70

after .24 .33 .34 1.43 1.43 1.89

2 of original I i D retained 23 21 19 93 69 The film units wereprocessed with Processing Composition A plus the indicated developersand 0.02

g./l cc. of processing composition of diamino orthocresol a 92 mg.silver/No gold compound s an auxiliary developer.

86.1 mg. silver/9.6 mg. gold Mcrcaptobenzimidazole Green Blue Red GreenBlue Tetrumethyl reductic acid mm n I (0.511 g/IO cc. of processingcomposition) before mm 1.40 1.97 2.60 i 1.64 2.03 2.76

after .95' 1.41 1.86 1.64 1.93 2.26

'7! of original D retained 65 72 72 99 100 82 .ASQQF LQBFl i I (0.6g./l0 cc. of processing composition) before test 1.5 5 0 206 l.64 1. 9 22:77 W

after .59 .93 1.16 2.26 2.23 1 3.06

"/1 of original I D,,,., retained 38 44 137 I 16 I 10 TABLE 2 m The filmunits were processed with Processing Composition B plus the indicateddevelopers and 0.02 g./l0 cc. of processing composition of diamineorthocresol as an auxiliary developer.

' 86.1 mg. silver/9.6 mg. gold harms raragara 65511411152 readily noted1115.

the previously described significant improval in silver transfer imagestability is directly achieved by means of the present invention whenthe exposed film unit is contacted with the described silver halidedeveloping agent and noble metal ions.

gold mercaptobenzimidazole as the noble metal ionproviding compound andcolloidal gold as the silver precipitating nuclei.

92 mg. silver/No gold compound Mercaptobenzimidazole Red Green Blue RedI Green Blue Toluhydroquinone (0.423 g./l0 cc. of processingcomposition) before test i 2.63 3.17 3.52 2.41 2.75 3.23

after 1.10 1.69 1.97 2.20 2.50 2.70

g Dim... retained 42 v 53 56 91 91 84* Dimethylhydroquinone I (0.47g./10 cc. of processing composition) before test 2.42 3.03 3.42 2.012.48 3.10 after .42 1.01 1.23 1.29 1.81 2.28 of original Dm retained 2133 36 .64 73 74 Tetramethyl reductic acid (0.589 g./ 10 cc. ofprocessing composition) before test 2.11 2.49 2.62 2.11 2.34 2.82 after1.59 1.98 2.22 2.09 2.35 2.54 of original D1,"... retained 75 s0 s5 1101 100 Ascorbic acid 1 (0.6 g./1O cc. of processing composition) beforetest 2.19 2.61 3.14 1.95 2.35 2.90 after 1.15 1.73 2.33 2.11 2.32 2.51of original Dmux retained 53 66 74 108 101 87 As; denoted abovei thphotosensitive silver halide stratum and/or the silver precipitatingnuclei containing stratum may have advantageously incorporated thereindiscrete particulate materials providing increased porosity to the filmunit, without deleterious effect on the dimensional stability of thebinder lattice, in particular, those materials which additionally act asan antiswelling agent for the binder material and, accordingly. act tofacilitate the prevention of thecarried image's microscopic distortion,particularly, with respect to an associated color screen, such asdiscrete silica particles 1 dispersed, for example, in a concentrationof about 0.3 to 1.5 silica per part binder, for the purpose offacilitating processing composition permeation of the film units silverhalide crystal and silver precipitating nuclei containing layer orlayers. In addition, the silver halide or silver precipitating nucleicontaining stratum may be advantageously overcoated with a processingcomposition permfiable PQlYF l Y F msts islsss t a h f gelatin pad orthe like to advantageously promote uniformity in processing compositionpermeation of such stratum, by modulating any wave front resultant frominitial surface contact with the liquid employed and to thereby promoteuniform maintenance of the poly meric binders physical characteristics.

Although chrome alum and particularly alg'in have been advantageouslyemployed as hardening agents for the polymeric gelatin emulsion binder,it will be recognized that substantially any hardening or crosslinkingagent may be employed, where necessary and with rethe extent required toprovide a' binder lattice which effectively inhibits to a substantialeffect, migration of image silver. An extensive collection of hardeningagents are disclosed in the art as specifically adapted to effecthandling or crosslinking of photographic polymeric binder materialcompositions-and by reason of their inocuous photographic effects are tobe preferred in the practice of the present invention. The sole retherelative activity of the selected agent, or agents, and

the relative amount of hardening or crosslinking to be effected. Thespecific concentration of a selective hardening or crosslinking agent,to be contacted with a selected polymeric binder, may be readilydetermined empirically, within the specific context of ultimatephotographic employment, by screening. lt-will be further recognizedthat any of the various processing composition permeable, syntheticornatural polymeric materials, possessing the physical characteristicsrequired to I provide the results denoted above, may be substituted inreplacement of the specifically illustrated polymeric materials providedwith such selected polymer provides a matrix which is not deleterious tophotosensitive silver halide crystals and possesses a lattice allowingprocessing in'the manner previously described.

Suitable silver halide solvents for employment in the practice of thepresent invention include conventional fixing agents such as thepreviously noted sodium thiosulfate, sodium thiocyanate, ammoniumthiocyanate, the additional agents described in US. Pat. No. 2,543,181,and the associations of cyclic imides and nitrogenous bases such asassociations of barbiturates or uracils and ammonia or amines and otherassociations described in US. Pat. No. 2,857,274.

Where desired conventional silver toning agent or agents may be disposedwithin the emulsion composispect to any one ormore layers of the filmunit, which does not provide deleterious photographic effects, to,

tion in a concentration effective to provide a positive inagatsaed inaessraaicanirtsesears;arise ope ator.

In the preferred embodiment of the present invention, the processingcomposition will include an alkaline material, for example, sodiumhydroxide, potassium hydroxide or sodium carbonate, or the like, and

most preferably in a concentration providing a pH to sition of one ormore developing agents in the emulsion and/or permeable layer. directlyassociated therewith, intermediate the emulsion and a color screen, is aparticularly preferred embodiment, for the purpose of providing enhancedimage acuity, by more readily facilitating directly initiateddevelopment at radiation exposed areas of the emulsion without thenecessity of diffusing such agents to such sites by means of theprocessing composition selected.

V The preferred silver halide developing agents generally compriseorganic compounds-and, in particular, comprise organic compounds of thearomatic series containing at least two hydroxyl and/or amino groupswherein at least one of such groups is in one of ortho or para positionswith respect to at least one other of such groups such as, for example,the various known hydroquinones, p-arninophenols, and their variousknown functional'hornologues and analogues.

It will be apparent that the relative proportions of the agentscomprising the processing composition set forth herein may be altered tosuit the requirements'of the operator, however, the processingcomposition solvent employed will generally comprise water and willpossess a solvent capacity which does not deleteriously hydrate theselected binder lattices beyond that required to provide the preferredimage formation. Accordingly, no adjunct should be included within suchcomposition which deleteriously effects the lattice parameters, requiredfor such image formation;

In the description herein, each color series of filter ,elements hasbeen described as covering that part of the total area in proportion tothe total number of colorsused, i.e., in thetricolor system, each coloroccupies one-third of the total area. This may vary quite widely beforehaving noticeable effect to the observer and, in fact, may becompensated by changing the intensity of the colors. In actual practice,if one dye is of greater intensity than the others, a deliberatecompenmary colors, red, green, and blue.

it will be recognized, however, that, in accordance with the instantdisclosure, a plurality of chromatic filter element series may beprovided, the number of series being solely determined by the opticalparameters of the resultant color screen desired.

For example, a four-color system such as red, green,

27 violet-blue and orang 'irdtvtild alsobe effectively employed inaccordance with the teachings of the instant disclosure.

In the practice of the present invention, additive trichromatic colorscreens possessing 550, 756, and 1125 triplets/inch may be readilyemployed and it has been found that image resolution obtained by meansof the present invention exceeds that obtainable in prior art processes.Such increased resolution specifically facilitates the acuity of colorreproduction to be achieved by the practice of the invention and thesilver halide stratum will be panchromatically sensitized to provideequal image production, as a direct function of incident exposingradiation, throughout the response portion of the radiation spectrum tofurther enhance the acuity of color information recordation by theemulsion.

' In addition to the described essential layers, it will be recognizedthat the film unit may also contain one or more subcoats or layers,which, in turn, may contain one or more additives such as plasticizers,intermediate essential layers for the purpose, for example, of enhancingadhesion, and that one or more of the described layers may comprise acomposite of twoor more strata which may be contiguous or separated fromeach other.

Since certain changes may be made in the above product, process andapparatus without departing from the scope of the invention hereininvolved, it is intended that all matter contained in the abovedescription shall be interpreted as illustrative and not in a limsense.i What is claimed is:

l. A photographic process which comprises, in combination, the steps of:

a. exposing a photographic film unit comprising photosensitive silverhalide;

b. contacting said exposed film unit with a processing compositioncontaining an a,B-enediol silver halide 1 developing agent, therebyproviding a visible silver "ima e to said uriit as a function of thepoint-topoint degree of exposure thereof; and

c. contacting said silver image with a noble metal ion below silver inthe Electromotive Force Series of Elements.

2. A process as defined in claim 1 wherein said processing compositionincludes a silver halide solvent and said visible silver image is formedby silver diffusion transfer and said film unit includes silverprecipitating nuclei.

3. A process as defined in claim 2 wherein said enediol silver halidedeveloping agent contains, in its molecular structure, a segment of theformula:

'diol silver halide developing agent includes in its molecularstructure. a segment of the formula:

H ball 5. A process as defined in claim 2 which comprises, incombination, the steps of:

a. exposing a photographic film unit comprising a transparent supportcarrying on a first surface a substantially photosensitive layercomprising silver precipitating nuclei and a photosensitive silver hal'ide layer comprising photosensitive silver halide crystals, and a noblemetal ion below silver in the Electromotive Force Series of Elements;

b. contacting said silver halide emulsion with an aqueous processingcomposition containing an a,B-enediol silver halide developing agent anda silver halide solvent for a period of time effective to provide avisible silver-image to'said film unit, as a function of exposure; and

c. coacting said silver image with a noble metal ion below silver in theElectromotive Force Series of Elements in a concentration effective toenhance the stability of said silver image.

6. A process as defined in claim 5 which comprises,

in combination, the steps of: e

a. exposing a photographic film unit which comprises a permanent fixedlaminate containing a transparent support carrying a trichromaticadditive color screen comprising red, green and blue optical filterelements, a substantially photoinsensitive layer comprising silverprecipitating nuclei dispersed in a processing composition permeablematrix, a photosensitive silver halide emulsion comprisingphotosensitive silver halide crystals dispersed in a processingcomposition permeable polymeric binder and anobel metal ion below silverin the Electromotive Force Series of Elements, said exposureaccomplished by actinic radiation transmitted through said screen;

b. contacting said silver halide emulsion with an aqueous processingcomposition containing an a,B-enediol silver halide developing agent anda silver halide solvent for a period of time effective to provide avisible silver image to said film unit, in terms of the unexposed areasof said emulsion, as afunction of the point-to-point degree of emulsionexposure, and coaction between said silver image and said noble metalion effective to enhance the stability of said silver image; and

c. maintaining said laminate intact subsequent to processing.

7. A process as defined in claim 6 wherein said developing agent istetramet'hyl reductive acid and said noble metal ion is gold ion.

8. A process as defined in claim 1 wherein said noble metal compound isan organometal compound of the formula:

wherein M is a noble metal ion below silver in the Electromotive ForceSeries of Elements and X is a ligand which provides a substantiallywater-isoluble, alkaline solution soluble complex.

9. A process as defined in claim 8 wherein M comprises gold, platinum orpalladium.

10. A process as defined in claim 9 wherein said gold is Au.

11. A process as defined in claim 9 wherein said gold is Au.

29 A silver dififiision transfer photographic process as defined inclaim 8 wherein X is selected from the group consisting of2-mercaptobenzimidazole, 1phenyl-5-mercaptotetrazole and N'-methyl-2-mercaptoimidazole.

13. A process as defined in claim 5 wherein said processing compositioncontains an auxiliary developing agent.

14. A process as defined in claim 13 wherein said auxiliary developingagent is diaminoorthocresol.

15. A photographic film unit comprising a permanent I laminate adaptedto be processed by diffusion transfer processing which comprises acommon transparent support carrying on one surface a layer comprisingsilver precipitating nuclei and a layer comprising photosensitive silverhalide crystals, and a noble metal below silver in the ElectromotiveForce Series of Elements, adapted to interact with a silver imageprovided by proterms of noble metal within the range of about 1% to 20%of the silver present as silverhalide.

cessing of the film unit, in a concentration effective to enhance thestability of said silver image and an 'a,B-enediol silver halidedeveloping agent.

16. A film unit as defined in claim 15 wherein said noble metal isdisposed in said layer containing said photosensitive silver halidecrystals.

17. A film unit as defined in claim '15 wherein said noble metal isdisposed in said layer containing said silver precipitating nuclei.

18. A film unit as defined in claim 15 which includes a processingcomposition permeable layer, said permeable layer having said r'ioblemetal disposed therein.

19. A film unit as defined in claim 15 which includes an additive colorscreen.

20. A film unit as defined in claim 15 wherein said a,B-enedioldeveloping agent contains, in its molecular structure, a segment of theformula:

24. A film unit as defined in claim 15 wherein said noble metal compoundpossesses the formula:

methyl reductic acid.

2. A process as defined in claim 1 wherein said processing compositionincludes a silver halide solvent and said visible silver image is formedby silver diffusion transfer and said film unit includes silverprecipitating nuclei.
 3. A process as defined in claim 2 wherein saidenediol silver halide developing agent contains, in its molecularstructure, a segment of the formula:
 4. A process as defined in claim 3wherein said enediol silver halide developing agent includes in itsmolecular structure, a segment of the formula:
 5. A process as definedin claim 2 which comprises, in combination, the steps of: a. exposing aphotographic film unit comprising a transparent support carrying on afirst surface a substantially photoinsensitive layer comprising silverprecipitating nuclei and a photosensitive silver halide layer comprisingphotosensitive silver halide crystals, and a noble metal ion belowsilver in the Electromotive Force Series of Elements; b. contacting saidsilver halide emulsion with an aqueous processing composition containingan Alpha , Beta -enediol silver halide developing agent and a silverhalide solvent for a period of time effective to provide a visiblesilver image to said film unit, as a function of exposure; and c.coacting said silver image with a noble metal ion below silver in theElectromotive Force Series of Elements in a concentration effective toenhance the stability of said silver image.
 6. A process as defined inclaim 5 which comprises, in combination, the steps of: a. exposing aphotographic film unit which comprises a permanent fixed laminatecontaining a transparent support carrying a trichromatic additive colorscreen comprising red, green and blue optical filter elements, asubstantially photoinsensitive layer comprising silver precipitatingnuclei dispersed in a processing composition permeable matrix, aphotosensitive silver halide emulsion comprising photosensitive silverhalide crystals dispersed in a processing composition permeablepolymeric binder and a nobel metal ion below silver in the ElectromotiveForce Series of ElEments, said exposure accomplished by actinicradiation transmitted through said screen; b. contacting said silverhalide emulsion with an aqueous processing composition containing anAlpha , Beta -enediol silver halide developing agent and a silver halidesolvent for a period of time effective to provide a visible silver imageto said film unit, in terms of the unexposed areas of said emulsion, asa function of the point-to-point degree of emulsion exposure, andcoaction between said silver image and said noble metal ion effective toenhance the stability of said silver image; and c. maintaining saidlaminate intact subsequent to processing.
 7. A process as defined inclaim 6 wherein said developing agent is tetramethyl reductic acid andsaid noble metal ion is gold ion.
 8. A process as defined in claim 1wherein said noble metal compound is an organometal compound of theformula: M-X wherein M is a noble metal ion below silver in theElectromotive Force Series of Elements and X is a ligand which providesa substantially water-isoluble, alkaline solution soluble complex.
 9. Aprocess as defined in claim 8 wherein M comprises gold, platinum orpalladium.
 10. A process as defined in claim 9 wherein said gold isAu
 1. 11. A process as defined in claim 9 wherein said gold is Au
 3. 12.A silver diffusion transfer photographic process as defined in claim 8wherein X is selected from the group consisting of2-mercaptobenzimidazole, 1-phenyl-5-mercaptotetrazole andN''-methyl-2-mercaptoimidazole.
 13. A process as defined in claim 5wherein said processing composition contains an auxiliary developingagent.
 14. A process as defined in claim 13 wherein said auxiliarydeveloping agent is diaminoorthocresol.
 15. A photographic film unitcomprising a permanent laminate adapted to be processed by diffusiontransfer processing which comprises a common transparent supportcarrying on one surface a layer comprising silver precipitating nucleiand a layer comprising photosensitive silver halide crystals, and anoble metal below silver in the Electromotive Force Series of Elements,adapted to interact with a silver image provided by processing of thefilm unit, in a concentration effective to enhance the stability of saidsilver image and an Alpha , Beta -enediol silver halide developingagent.
 16. A film unit as defined in claim 15 wherein said noble metalis disposed in said layer containing said photosensitive silver halidecrystals.
 17. A film unit as defined in claim 15 wherein said noblemetal is disposed in said layer containing said silver precipitatingnuclei.
 18. A film unit as defined in claim 15 which includes aprocessing composition permeable layer, said permeable layer having saidnoble metal disposed therein.
 19. A film unit as defined in claim 15which includes an additive color screen.
 20. A film unit as defined inclaim 15 wherein said Alpha , Beta -enediol developing agent contains,in its molecular structure, a segment of the formula:
 21. A film unit asdefined in claim 20 wherein said segment is part of an heterocyclicstructure.
 22. A film unit as defined in claim 20 wherein said segmentis part of a carbocyclic ring.
 23. A film unit as defined in claim 15wherein said noble metal compound is present in a concentration in termsof noble metal within the range of about 1% to 20% of the silver presentas silver halide.
 24. A film unit as defined in claim 15 wherein saidnoble metal compound possesses the formula: M-X wherein M is a noblemetal below silver in the Electromotive Force Series of Elements and Xis an organic ligand which provides a substantially water-insolublecomplex.
 25. A film unit as defined in claim 24 wherein X is2-mercaptobenzimidazole, 1-phenyl-5-mercaptotetrazole orN''-methyl-2-mercaptoimidazole.
 26. A film unit as defined iN claim 24wherein M comprises gold, platinum or palladium and said Alpha , Beta-enediol silver halide developing agent is tetramethyl reductic acid.